Conventional video cassette recorders (VCRs) can implement a one-time record (OTR) feature where a user starts recording current program material at a current location on the tape cassette. Since conventional VCRs do not buffer program material prior to the activation of the recording feature, material prior to activating the recording is not captured. Consequently the first part of a program is often lost, as the user typically decides to activate a one-time recording after a particular program has begun. Recording only a portion of desired program material is unattractive to the user.
Current hard disk drive based digital video recorder (DVR) or personal video recorder (PVR) products tend to emulate the behavior of a VCR. However, unlike a VCR, some portion of the program material prior to the activation of one-time recording has usually been buffered within the DVR.
A DVR typically has two modes of recording operation (i) time shift mode and (ii) background record mode. The time shift mode entails recording a program currently being broadcast for short term manipulation at the convenience of the user. Examples of short term manipulation include pausing the current program (perhaps in response to an external interruption) or instant replay of a sequence in the current program (perhaps a personalized review of important action in a sporting event).
During time shift, the current program is recorded to a time shift buffer. Since the user may rewind (or review) the program at any time, the current program is always being recorded, even when it is being watched live. When the length of the time shift operation exceeds the length of the time shift buffer, the DVR writes the more recent program material over the oldest material in the time shift buffer. Consequently, the short term manipulation is limited to that portion of the current program material stored in the time shift buffer. The short term manipulation creates a lag between the real time broadcast of the program and the point in the program currently being displayed.
In the case of the pause operation, either the operation may be limited to the length of the time shift buffer, such that the material being displayed when the pause operation was started is overwritten with newer program material when the limit of the time shift buffer is reached, or the operation may cause the time shift buffer to be expanded (subject to available storage space), such that a time-shifted program will have the program material wholly contained within the time shift buffer prior to the pause point and the additional program material recorded between the pause point and the live program broadcast.
The background record mode entails the recording of an entire broadcast program for playback at a later time. Recording is initiated at a fixed time, set by the user either directly by channel, time and duration, or indirectly via an electronic program guide (EPG). The user may watch the program being recorded (in real time, or with some time delay) or watch a different program. During background record, the program is recorded to a linear buffer. The length of the program to be recorded dictates the length of the buffer (assuming sufficient space is available) Normally, the buffer is only overwritten if the program is erased and the space is freed for a later recording.
If the user activates a one-time record, the conventional DVR will switch from time shift mode to background record mode. The DVR will then record to the linear background record buffer in place of the circular time shift buffer. The program material contained in the time shift buffer will not be preserved in a conventional DVR.
It would be desirable to implement a personal video recorder that would retroactively record all or part of a live/time-shifted program after the program has begun.